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Electrical Circuits Energy transfer in circuits Energy cannot be created or destroyed. In all devices and machines, including electric circuits, energy is transferred from one type to another. When this circuit is connected, chemical energy stored in the battery is transferred via electrical energy to heat and light energy in the bulbs. The total amount of heat and light energy is the same as the amount of chemical energy lost from the battery. Energy transfer in electrical circuits 5 J transferred to bulb as light energy chemical energy from battery (e.g. 100J) 95 J transferred to heat energy of bulb Most of the energy from the battery does not produce light – most of it is wasted as heat! What is the energy transfer? Batteries can power many electrical devices. What sort of energy is electrical energy transferred into in these electrical devices? What is an electrical circuit? An electrical circuit is like a central heating system in a house. There is a pump that pushes water around the system. The water everywhere starts to move at the same time. There are pipes that carry the water. In the pipes the water is flowing. low pressure boiler and pump high pressure radiator radiator flow of water What is an electrical circuit? The bulb in the circuit is like a radiator. An electrical device uses electrical energy supplied by the circuit. Instead of a flow of water, electricity flows in an electrical circuit. The wires are like pipes; they carry the flow of electricity (called current) around the circuit. The electrical current is pushed by the cell (or battery), which has the same function as the pump and boiler. The strength of push provided by the battery is called its voltage. Drawing Circuits 1) A battery, a bulb and a switch ‘in series’ 2) A battery of cells, a switch and two bulbs in series Components in an electrical circuit Measuring current The unit of measure for current is the amp, which has the symbol A. Current is measured using a device called an ammeter. In a circuit diagram, an ammeter is shown by the symbol A . When measuring the current through a component, the ammeter is always connected in series (in the same loop) with that component. A Current in a series circuit If the current here is 2 amps… The current here will be… The current here will be… And the current here will be… In other words, the current in a series circuit is THE SAME at any point Changing the current If a battery is added the current will ________ because there is a greater _____ on the electrons. If a bulb is added the current will _______ because there is greater ________ in the circuit What is a series circuit? This is a simple series circuit. In a simple series circuit, everything is connected in one loop across the terminals of the battery. So there are not any points where the current can split or join (these are called junctions). This circuit has two lamps connected in series. Circuits are always drawn using straight lines. Examples of series circuits Here are some other simple series circuits: 1. Two resistances (resistors) connected in series: R1 R2 2. A rheostat (or variable resistor) and a bulb connected in series: Series circuits – key ideas 1. In a series circuit the current is the same in all parts of the circuit. 2. The supply voltage is shared between the components in a series circuit. (The sum of the voltage across each component is the same as the total supply voltage.) 3. The current depends on the voltage in any circuit. Current in a parallel circuit A parallel circuit is one where the current has a ‘choice of routes’. Here comes the current… Half of the current will go down here (assuming the bulbs are the same)… And the rest will go down here… Current in a parallel circuit If the current here is 6 amps And the current here will be… The current here will be… The current here will be… The current here will be… Advantages of parallel circuits… There are two main reasons why parallel circuits are used more commonly than series circuits: 1) Extra appliances (like bulbs) can be added without affecting the output of the others. 2) If one appliance breaks it won’t affect the others either. Comparing series & parallel circuits Series circuit Parallel circuit If one bulb blows they all go out. If one bulb blows only that one goes out. One switch operates all of the bulbs. Each bulb can be turned on and off with its own switch. The voltage across the power supply is shared between all of the bulbs. The voltage across each bulb is the same as across the power supply. The current from the power supply is low. The current from the power supply is high. Measuring voltage Voltage is measured using a device called a voltmeter. In a circuit diagram, a voltmeter is given the symbol V . When measuring the voltage across a component, the voltmeter is always connected in parallel with (or across) the component. V 1 This is still a series circuit. V2 V3 The voltage supplied by the battery is shared between all the components in a series circuit. Measuring voltage across a resistance or a bulb Voltage is measured by connecting the voltmeter across (or in parallel with) the component. V Voltage is measured in volts and the symbol for this is V. A Components component here V R Wiring a plug Earth wire Live wire Fuse Neutral wire Insulation Cable grip Fuses Fuses are _______ devices. If there is a fault in an appliance which causes the ____ and neutral (or earth) wire to cross then a ______ current will flow through the _____ and cause it to _____. This will break the _______ and protect the appliance and user from further _____. Words – large, harm, safety, melt, live, circuit, fuse Earth wires Earth wires are always used if an appliance has a _____ case. If there is a _____ in the appliance, causing the live wire to ______ the case, the current ‘_______’ down the earth wire and the ______ blows. Words – fuse, fault, metal, surges, touch Circuit breakers If the current becomes too high the __________ is activated. This will ______ the iron and the contact will be _______. This will break the circuit. Circuit breakers have two main advantages over fuses: they work ______ and can easily be ______. Words – electromagnet, broken, attract, reset, quicker Multiple Choice Quiz